The present invention relates to a vibration motor assembly for use in a portable phone or similar mobile communication apparatus.
Mobile communication apparatuses extensively used today include portable phones, PHS (Personal Handyphone System) terminals, and radio pagers. The major advantage of a mobile communication apparatus is that the apparatus, in principle, can be used at any desired place. This, however, brings about a problem that the apparatus receives a call even in a train, theater or similar public space and produces an annoying alert tone. To solve this problem, the apparatus is usually provided with a silence mode for producing no alert tones in the event of call incoming or call receipt, a vibration mode for producing an alert in the form of vibration, and a memory phone function.
The vibration mode, among others, is often used because it allows the user of the apparatus to see call incoming or call receipt immediately without annoying the others. The vibration mode is generally implemented by a vibration motor assembly built in the apparatus. In the event of call incoming, for example, the vibration motor assembly is caused to vibrate in order to alert the user to the call incoming.
While the vibration motor assembly has been proposed in various forms in the past, it basically consists of a motor and a weight formed of, e.g., metal and directly mounted on the output shaft of the motor in an eccentric position. When the motor is rotated, vibration occurs due to the inertial force of the eccentric weight. However, a problem with this type of assembly is that a great initial torque and therefore a great initial current is necessary for the weight held in a halt to start rotating by overcoming the eccentricity. A sufficient initial current is not available with a miniature battery powering the above apparatus, making it difficult to start the vibration of the assembly. To reduce the required initial current, the eccentricity or the weight of the weight may be reduced. This, however, gives rise to another problem that vibration intense enough to surely alert the user to, e.g., call incoming is difficult to achieve. It is therefore difficult to implement a small initial current for driving the assembly and a sufficient degree of vibration at the same time.
Japanese Patent Laid-Open Publication Nos. 2-111269 and 63-262069, for example, each disclose a vibration motor assembly using a piezoelectric element in place of the ordinary motor. The piezoelectric element, constituting a drive source for vibration, is caused to vibrate by an ultrasonic wave. This type of assembly has a drawback that the piezoelectric element sophisticates the construction of the assembly and thereby increases the cost of the same.
Japanese Patent Laid-Open Publication No. 7-227061 and Japanese Utility Model Laid-Open Publication No. 4-12486 each teach a vibration motor assembly including a weight and reducing the required initial current by moving it with a centrifugal force. In this type of assembly, the weight is initially positioned in the vicinity of the output shaft of a motor, but sequentially moved away from the shaft due to a centrifugal force as the rotation speed of the motor increases. The assembly therefore reduces the required initial current and finally implements a sufficient degree of vibration. However, this kind of scheme is not practicable without resorting to a mechanism for movably supporting the weight and a mechanism for returning the weight to its original position, resulting in a complicated construction and a high cost. Moreover, such an assembly is susceptible to shocks and impacts and not feasible to, e.g., a mobile communication apparatus which is likely to fall by accident.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Utility Model Laid-Open Publication No. 4-124862 and Japanese Patent Laid-Open Publication Nos. 8-33265 and 9-149591.